Thanks for the report!
Dou you know the game ID where that happened? That allows me and others to look at the situation and see what happened.
The only explanations I can come up with is that
a) you took a $5 cost Knight, the next Knight was Sir Martin (costs $4) and there was only one other pile with a $5 cost card on top (which the game gaves you automatically), or
b) you took Sir Martin (costs $4), so the next Knight costs $5 and there was only one other pile with a $4 cost card on top (which the game gaves you automatically).
